Apparatus for controlling the atmosphere in an electric furnace



4 Sheets-Sheet 1 R. J. GARMY Sept. 13, 1960 APPARATUS FOR CONTROLLINGTHE ATMOSPHERE 1N AN ELECTRIC FURNACA:

Filed July 1o, 1957 l N V EN TOR. A9055@ J @www BY I LJ, /J W ,4T'/P/VFV R. J. GARMY Sept. 13, 1960 APPARATUS FOR CONTROLLING THEATMOSPHERE IN AN ELECTRIC FURNACE 4 Sheets-Sheet 2 Filed July lO, 1957Sept. 13, 1960 R. .1. GARMY 2,952,723

APPARATUS FOR coNTRoLLING THE ATMOSPHERE 1N AN ELECTRIC FURNACE:

Filed July 1o, 1957 4 sheets-sheet s L B3n A/ JMW i i INVENTOR.

Sept. 13, 1960 R. .1. GARMY 2,952,723

APPARATUS RoR CORTROLLIRG THR ATMOSPHERE 1N AN ELECTRIC RURNACE FiledJuly lO, 1957 4 Sheets-Sheet 4 Ti. E.

United States Patent() APPARATUS FOR CONTROLLING THE ATMOS- PHERE IN ANELECTRIC FURNACE Filed July 10, 1957, Ser. No. 670,921

4 Claims. (Cl. 1333) This application is a continuation-in-part of mycopending application, Serial No. 391,549, filed November 12, 1953,entitled Method and Apparatus for Forming Ingots, now Patent No.2,800,519, dated Iuly 23, 1957.

This invention relates to' a method and apparatus for controlling theatmosphere in an electric furnace.

In order to obtain metal in Ia form which may be worked, i.e., rolled,forged, etc., in conventional fashion, it is rst necessary to form ahomogeneous ingot, usually by melting a quantity of the metal in afurnace. For products of the greatest purity, electric furnaces arepreferred. v

'Metals are generally quite impure in the form in which they are rstobtained by reduction from their ores. Titanium and zirconium,.forexample, are commonly obtained by reduction from their respectivechlorides, with magnesium as the reducing agent. The resulting metalcommonly contains magnesium chloride as an impurity.

That material, and other common impurities, vaporize lat thetemperatures required in the melting furnace. These vaporized impuritiesinterfere with normal furnace operation and tend to condense on and foulthe cooler surfaces in the furnace structure where the melting operationis taking place. Furthermore, if these impurities are allowed to remain,they may contaminate the ingot, making objectionable flaws therein.

This invention is particularly concerned with controlling the atmospherein such a furnace by maintaining it chemically inactive (i.e., ofhelium, argon, or the like), and by removing from the atmosphereimpurities originating in the charge of material being treated, whichimpurities are volatile at the temperatures employed in the furnace.

The invention is of particular utility in the treatment of metals suchas titanium and zirconium and their alloys. It is of more generalutility in connection with the manufacture of ingots from other metals,e.g., steel, Where a product of high purity is required.

An object of the present invention is to provide improved methods andapparatus for producing homogeneous ingots of metals such as titaniumand zirconium.

Another object is to provide an improved electric furnace.

Another object is to provide improved apparatus for maintaining an inertgas atmosphere in an electric furnace during its operation.

Another object of the invention is to provide an improved method ofcontrolling the pressure of an inert gas in a furnace for melting ametal such :as titanium or zirconium.

Another object is to provide an improved method of circulating an inertgas through a space in which a metal such as titanium or zirconium isbeing melted.

A further object is to provide an improved method for removingimpurities from such a metal by condensing vapors from the circulatinginert gas.

These objects are attained by providing apparatus for circulating aninert gas, for example, helium, argon, or a mixture of both, through thefurnace while it is operat- ICC ing. The inert gas leaving the furnacepasses through a condenser where it is cooled so that the vapors andimpurities picked up in the furnace are deposited in the condenser. Thecooled gas is then returned to the furnace where it is used to co'olvital parts and to displace contaminated gas.

Apparatus is provided for maintaining the pressure within the furnacewithin the range from about three to about five ounces per square inchabove atmospheric pressure. This range is high enough to ensure thatthere are no air leaks into the furnace, while at the same time it isnot high enough to' cause absorption of the gas into the ingot, withresulting formation of iiaws or other inhomogeneities therein.

Other objects and advantages of the invention will be come apparent froma consideration of the following description and claims, together withthe accompanying drawings.

In the drawings:

Fig. l is a somewhat diagrammatic illustration, partly in section andpartly in elevation, of a furnace equipped with pressure controlapparatus according to one feature of the invention;

Fig. la is a fragmentary View, similar to a portion of Fig. l, showing amodification;

Fig. 2 is a -somewhat diagrammatic elevational view of a furnaceequipped with gas circulating `apparatus according to another feature ofthe invention;

Fig. 3 is a plan view of the apparatus of Fig. 2;

Fig. 4 s a view, principally in section, on the line IV-IV of fFig. 5,and partly in elevation, `with certain parts broken away, showing afurnace shell and gas inlets and outlets therefor; and

Fig. 5 is a fragmentary `sectional view on the line V-V of Fig. 4.

The furnace illustrated herein is more completely described in mycopending application Serial No. 391,549, now Patent No. 2,800,519,identified above. Only those parts of the furnace which are essential toVan understanding of the present invention will be described in detailherein.

The furnace is generally indicated by the reference numeral 1; itcomprises a cylindrical shell 2, open at the bottom, and a crucible 3,also cylindrical, located below the open bottom of the shell Z.

The metal to be melted to form an ingot is supplied in the form ofparticles or sponge from any suitable feeding mechanism into a feed pipe4 (Figs. 4 and 5), which leads through a wall of the shell 2 anddelivers the particles into a hopper 5 attached to a hollow central tube6. The hopper has an opening at its bottom aligned with an opening 6a inthe tube. The tube is open at the bottom and the particles fall throughit into the center of the crucible 3, forming a pile 8 (Fig. l).

A plurality of electrodes 7 (Fig. l) extend downwardly into theCrucible. A source of electrical energy (not shown) is connected to theelectrodes 7 and to the walls of the Crucible, and forms an arc -betweenthe electrodes and the charge in the ciucible, thereby melting the par@ticles to form a pool 9 of molten metal just below the electrodes. TheCrucible 3 is double-walled to provide cooling jackets, and the poolcools and solidifies to form an ingot 10. The electrodes are raised asthe material is fed in to maintain a more or less constant arc lengthbetween the electrodes and the pool surface.

Pressure regulating apparatus-Fig. 1

Fig. 1 illustrates appar-atus for maintaining in the furnace 1 anatmosphere of inert gas at a regulated pressure. As there shown, thepressure regulating apparatus in cludes a resorvoir 11 which mayrepresent a commercial cylinder of argon or helium gas, or a pluralityof cylinders providing a mixture of the two gases. The gas from thereservoir 11 ows through a constant pressure regulating valve 12 to oneof the inlet pipes 13 described below in connection with'Figs. 2 and 3.The pressure regulating valve 12 is controlled by the pressure in astatic pressure line 14 connected to the interior ofthe furnace shell 2.The arrangement is suchthat gas is admitted from the resorvoir 11 to thefurnace shell 2 whenever the pressure in that shell drops below apredetermined value. Excessive pressures in shell 2 are prevented by aoontrolled venting arrangement, including a vent pipe 15 leading fromthe interior of the shell 2 to a trap 16. From the trap 16 a pipe 17leads to a water bubbler pressure control mechanism 18. The controlmechanism 1.8 includes a container 19.mounted on a bracket 20 whosevertical position relative to the lower end of the pipe 17 may beadjusted by means of a suit-able screw and slot arrangement 21. Thecontainer 19' is provided with an overilow port 19a which determines thelevel of the water in the container. Water is continuously trickledi'nto the container through a pipe 22. The mechanism 18 maintains aiixed back pressure in the pipe 17. The water supply pipe 22 maintainsthe level in the container 19 even though some of the water therein maybe sucked back through the pipe 17 upon a sudden drop in pressure in theshell 2. The trap 16 prevents any water which is sucked back in thatmanner from reaching the shell 2.

A pressure in the range between three and five ounces per square inchabove atmospheric pressure is employed. A pressure of at least threeounces per square inch is a safety precaution which eliminates allpossibility of leakage of air into the furnace. Furthermore, the upperylimit of this range is quite critical withy regard to the quality ofproduct. If a higher pressure is used, it has been found that gasocclusions occur inthe ingot, which result in metallurgical defects inthe finished product, namely scabs, slivers and laminations.

The equipment is adaptable with slight modications shown in Fig. la,namely the addition of a vacuum pump 40 and elimination of the bubblerventing arrangement, to operation at pressures less than atmospheric,for purposes of reducing ingot hydrogen, for example. In such cases, theimpurity (hydrogen) cannot be economically condensed or otherwiseremoved, and it is therefore in most cases not economical to recirculatethe gas removed from the furnace.

lnert gas @circulating system-Figs. 2 and 3 Figs. 2 and 3 illustrate,somewhat diagrammatically, a. system for circulating an inert gas, forexample helium, argon, or a mixture of the two, through the furnaceshell 2 and thereby through the crucible during operation of thefurnace.l v

It has been found that titanium which has been reduced from titaniumtetrachloride by use of magnesium contains magnesium and magnesiumchloride as impurities. When operating a furnace of the type describedto form an ingot of titanium, these impurities vaporize at the hightemperatures used for melting the titanium. If not removed from thefurnace, these vapors adversely affect the stability of the arcs, andalso tend to condense on the cooler parts of the furnace, therebyfouling those parts.

In accordance with the present invention, apparatus is provided forcirculating inert gas through the furnace during its operation. In anyoperation involving titanium or zirconium, the gas must be one of thetruly inert gases which cannot combine chemically with the titaniumunder any circumstances. Titanium, especially at high temperatures inthe neighborhood of its melting point, is very active chemically and,with few exceptions, will cornbine with any element with which it isassociated. Since helium and the other inert gases are quite expensive,it is desirable to recirculate the gas.

L In the furnace shell 2 and its associated apparatus, therevareprovided a number of gas inlets, including a gas 4 inlet pipe 20 (seeFig. 4) which directs cooled gas into a heat shield around the outsideof the hopper 5. Gas inlets 22 are provided in connection with threeperipheral sight tubes 23 and a gas inlet 24 in connection with thecenter tube 6 which also serves as a sight tube. A heat shield tube 25around the feed pipe 4 is also provided with a gas inlet 26 (Fig. 5).

Aid these gas inlets are `shown in. Figs. 2 and 3. There are also shownin Fig. 3 two gas outlets 27 from the furnace shell 1. A dual gascirculatingY system is shown, the apparatus being duplicated for eachoutlet. Gas leaving either outlet 27 passes through a valve 28 andthence through a condenser 29, a pump 30 driven by a motor 31 and thencethrough a discharge conduit or manifold 13 provided with branch conduits(leading to the various gas inlets associated with the furnace shell 2.Each half of the dual system serves one groupof gas inlets to the shell2, and one of the two voutlets 27. It will be readily appreciated that asingle system of suiiicient capacity could be used. in place of the dualsystem shown. The dual system was selected for the installation shownfor reasons of convenience and economy and with regard to thespaceavailable. Each .condenser 29 has a water inlet 32 and a water outle-t33. The condenser cooling coils are removable from the gas circulatingsystem during periods of shut. down, in order to clean the. deposits ofmagnesium and magnesium chloride from the cooling coils. Y The inert gascirculating system serves to remove impurities such as magnesium andmagnesium chloride and prevent their inclusion in the finished ingot.Further more, when the gascirculating system is operated at a pressuregreater than atmospheric, the inert gas prevents oxygen, nitrogen andother chemically active constituents of the atmosphere from coming incontact with the molten titanium, which might otherwise become contain?inated with such constituents.

' Although the gas pressure regulating system of Fig. l-

is not shown in Figs. 2 and 3, it should be understood that a completesystem would preferably include both the pressure regulating system ofFig. 1 and the gas circulating system. of Figs. 2 and 3.

Details of shell-Figs. 4 and 5 The titanium sponge fed to the furnace ina continuous stream, preferably from a vibratory feeder (not shown) ofany suitable commercial type. The feeder ydischarges through the feedpipe 4 (see Fig. 4). The feed pipe 4 extends through the shield pipe 25which is mounted in the side wall of the furnace shell 1. A ilexiblecoupling 34 connects the feed pipe l4 with the stationary shield pipe25.

vThe electrodes 7 extend into the furnace through a head 35 which may beoscillated by means of a motor 36. At the center of the head 35 the tube6 projects downward insidefthe shell 2. Supported on the outside of thepost 6 is the hopper 5. The hopper 5 is generally sector shaped in itshorizontal cross-section, as maybe seen in Fig. 5. Its upper end extendsradially out from the hol-low pos-t far enough so that its periphery isbelow the inner end of the feed pipe 4.

As shown in Fig. 5, one of the electrodes 7 extends ver` ticallydownward through the hopper 5. In order to permit this, the hopper ismade in right and left-hand sections, each with ay recessed face whichtogetherdeiine a sleeve to permit free passage of the electrode 7. Theheat shield 21 (Fig. 4) generally conforms to the shape of the hopperand is spaced fromvit by a short distance. The nozzle 20 projectsthrough the side of the shell 1 and 'terminates at a point directlyopposite the opening between the upper'` end of hopper 5 and heat shield21. As described above, the nozzle 20 receives a continuous supplyofcooled inert gas, for example, helium, which is directed into the lspacebetween the heat shield andthe hopperA and passes kdownwardly throughthat space and out the lower end thereof. A collar 37 is mounted on thelower end of the tube 6 and is concentric with the tube and spacedoutwardly from it. The upper end of the space between tube 6 and collar37 is directly opposite the lower end of the space between heat shield21 and hopper 5 so that the ow of cool gas passing through that spacetends to continue through the space around the lower end of the tube 6.It may therefore be seen that all the parts through which the titaniumsponge passes on its way to the center of the Crucible are cooled by gasjackets and shields. These parts include the feed pipe `4 cooled by thegas flowing through shield pipe 25, the hopper 5 cooled by gas flowingthrough 'the shield 21 and the :lower end of the tube 6 cooled by gasflowing through the shield 37. The shields are also effective inreducing radiated heat. This cooling action prevents the metal particlesfrom becoming tacky and clogging the feed mechanism.

The cooled gas entering the various inlets tends to move by convectiondownward toward the locality of the arc in the Crucible, whereas the gasheated by the arc and the vaporized impurities tend to move upward, alsoby convection. There is thus maintained in the crucible a lflowingcurrent of gas tending to carry the impurities away from the arc and theforming ingot.

Cooled gas entering the inlets 22 maintains a ow through each sight tubein a direction away from the glass, thereby preventing fogging of theglass by condensation of vaporous impurities from the furnace.

By feeding the material through the side of the shell 2, interferencewith the oscillating head 35 and other mechanism (not shown) on andabove the head is avoided.

I claim:

1. An electric furnace comprising a generally cylin `drical shell, meansfor feeding material to be treated in the furnace to a central localitythereof, said feeding means comprising a hopper within said shell, aheat shield generally conforming to the outer wall of the hopper andspaced outwardly therefrom tol provide an open space between said outerwall and the heat shield, a condenser spaced from said shell for cooling-a gas flowing therethrough, means for circulating an inert gas throughthe shell and the condenser to pick up vaporous impurities in the shelland remove them by condensation in the condenser, and means forrecirculating cooled gas from the condenser back to the shell, saidrecirculating means comprising means for directing a iiow of cooling gasinto said open space.

2. An electric furnace as defined in claim 1, in which said feedingmeans comprises a hollow center post projecting downwardly within `saidshell and open at its lower end, and said recirculating means comprisesmeans for directing a ow of cooling gas downwardly through said hollowcenter post.

3. An electric furnace comprising a generally cylindrical shell, meansfor feeding material to be treated in the furnace to a central localitythereof, said feeding means comprising a hollow center post projectingdownwardly within said shell and open at its lower end, a feed pipeextending through a side of the shell and having its inner end open andspaced `from the center post, a heat shield tube encircling the feedpipe and open at its inner end, a hopper mounted on the center post andhaving an upper peripheral portion underlying the inner end of the feedpipe, said hopper and post having aligned openings and providing a path`for the material from the feed pipe through the hopper and into` thecenter of the hollow post, a heat shield generally conforming to theouter wall of the hopper and spaced outwardly therefrom to provide anopen space between the outer wall and the heat shield, a condenserspaced from said shell for cooling a gas flowing therethrough, means forcirculating an inert gas through the shell and the condenser to pick upvaporous impurities in the shell and remove them by condensation in thecondenser, and means for recirculating cooled gas from the condenserback to the shell, said recirculating means comprising means fordirecting flows of cooling gas into said open space, into the spacebetween the heat shield tube and the feed pipe, and into said hollowpost.

4 An electric furnace as dened in claim 3, including a collar encirclingthe lower end of the hollow post and cooperating therewith to deiine anannular passage, said passage having its upper end open and adjacentsaid open space to receive a current of cooling gas therefrom.

References Cited in the file of this patent UNITED STATES PATENTS2,564,337 Maddex Aug. 14, 1951 2,709,842 Findlay June 7, 1955 2,734,244Herres Feb. 14, 1956 2,762,856 Newcomb et al. Sept. 1l, 1956 2,816,828Benedict et al. Dec. 17, 1957 OTHER REFERENCES Journal of Metals, April1950, pages 634-640.

